class_docstr: test mixin with layout properties
code: def test_validate_properties(self):
      prop_obj = self.DummyTemplate()
      for prop in LayoutProperties.align_items.values:
          prop_obj.align_items = prop
          assert prop_obj.align_items == prop
  
      with pytest.raises(traitlets.TraitError):
          prop_obj.align_items = "any default position"
  
imports: from unittest import TestCase
  from unittest import mock
  import pytest
  import traitlets
  import ipywidgets
  from ipywidgets.widgets.widget_templates import LayoutProperties
label_desc: Use image node_id 3 for calling the TestLayoutProperties obj's underlying member method code with example usage: obj.test_validate_properties() without return types